On-site measurement and location of partial discharges in transformers without the need of special HV supply

Partial discharge (PD) measurement and location tests, especially for large transformers, require a high-voltage (HV) supply that is free from PDs, making it difficult for such tests to be performed on site. The author presents test circuits for testing three-phase and single-phase transformer banks with an on-load tap changer (OLTC). In both cases, the test voltage supplies the excitation as well as the supporting voltages. The author also describes an ultrasonic method of locating PDs for transformers using switching surges.<>